Corrosion Effects on Fracture Toughness Properties of Wire Arc Additively Manufactured Low Carbon Steel Specimens

The emerging wire + arc additive-manufacturing (WAAM) technique has significant potential to improve material design, as well as manufacturing cost and efficiency of structural components such as offshore wind turbines and subsequently reduce the levelised cost of energy (LCoE). Welded joints in offshore structures are usually considered potential spots for crack initiation due to the combination of high stress concentration at the weld toes, residual stresses introduced by the welding process and cyclic loading conditions in harsh, corrosive marine environments. The WAAM technique is a deposition method consisting of repetitive welding process that can be used as an alternative manufacturing technique for fabrication or repair of structural components. An important issue that needs to be understood in structural-integrity assessment of WAAM-built components is fracture-toughness behaviour. In particular, the sensitivity of fracture-toughness properties to corrosive environments must be examined in order to extend the application of the WAAM technique to offshore wind structures. Therefore, in this study, fracture-toughness tests were conducted on WAAM-built compact-tension specimens made of ER70S-6 and ER100S-1 steel that were initially exposed to a seawater corrosive environment prior to testing. All fracture-toughness tests were performed at room temperature, and crack length was estimated using the compliance method with a clip gauge attached onto the knife edge of the specimens. The obtained results, which include load vs. load-line displacement and J-integral vs. crack extension, were analysed and compared with the results of tests in air, without any exposure to seawater. The conclusions of this study show that corrosive environments affect the yield stress and R-curves of the selected materials and contribute to the overall understanding of the design requirements for functionally graded structures fabricated by means of WAAM technique for offshore applications.